We present high-resolution Magellan/MIKE spectroscopy of the brightest star in the ultra-faint dwarf galaxy Leo IV .
We measure an iron abundance of [ Fe / H ] = -3.2 , adding to the rapidly growing sample of extremely metal-poor stars being identified in Milky Way satellite galaxies .
The star is enhanced in the \alpha elements Mg , Ca , and Ti by \sim 0.3 dex , very similar to the typical Milky Way halo abundance pattern .
All of the light and iron-peak elements follow the trends established by extremely metal-poor halo stars , but the neutron-capture elements Ba and Sr are significantly underabundant .
These results are quite similar to those found for stars in the ultra-faint dwarfs Ursa Major II , Coma Berenices , Boötes I , and Hercules , suggesting that the chemical evolution of the lowest luminosity galaxies may be universal .
The abundance pattern we observe is consistent with predictions for nucleosynthesis from a Population III supernova explosion .
The extremely low metallicity of this star also supports the idea that a significant fraction ( \gtrsim 10 % ) of the stars in the faintest dwarfs have metallicities below [ Fe / H ] = -3.0 .